Both concern over health and the environment have led to interest in human powered recumbent vehicles. Long distance riding of regular bicycles is tiring not only in the arms and the posterior, but is also difficult for some people who find that the heads up position causing the neck to be bent backward results in pinched nerves. In addition, a three wheel recumbent type of cycle offers much increased safety from a stability point of view. An example of these advantages is set in a front wheel recumbent tricycle termed the Cyclodyne, disclosed in the Carpenter Patent 4,456,277.
Three wheeled recumbent human powered vehicles also offer many advantages from the point of view of energy consumption, particularly for third world countries as work vehicles.
In addition to the Carpenter cyclodyne and a small-wheel sport tricycle vehicle known as the Corsa, there is a wide variety of recumbent tricycles including the following: Forbes et al U.S. Pat. No. 4,497,502 shows a single front wheel, front drive HPRT in which the two rear wheels are steerable; Hendrix U.S. Pat. No. 4,373,740 shows a single rear wheel, rear drive HPRT in which the two front wheels are connected to a single crossbrace that prevents front access to the seat; Samuel U.S. Pat. No. 4,691,930 shows a push-type child's tricycle (1 front wheel, 2 rear) of modular construction that permits assembly into a variety of configurations; Feikima et al U.S. Pat. No. 4,432,561 shows a single front wheel front drive HPRT in which the front wheel is tilted, steered by shifting body weight relative to fixed rear wheels, and the crank is forward of the front wheel; Blease U.S. Pat. No. 4,079,957 shows a child's single front wheel tricycle that is convertible from a stranded high seat to a low rider (Big Wheel type), and the front wheel is directly cranked in both cases; Brummer U.S. Pat. No. Des 301,130; 304,319; and 327,040 all show various frames for recumbent bicycles, of which 304,319 has a single wheel rear drive with a crank forward of the front wheel; and Lemle U.S. Pat. No. 4,878,684 shows a rear drive recumbent bicycle with the crank intermediate the front wheel and seat, in which the seat is adjustable, and the vehicle is steered by under-seat handlebars.
The Carpenter Cyclodyne and the Corsa vehicle have the disadvantage in that the two front wheels are located on a cross axle or cross frame member which is well forward of the front lip of the user's seat. In essence these vehicles are very difficult to mount or dismount. For example, in order to mount the Carpenter cyclodyne one must step over the high lip of the fairing, place one foot on the center of the seat while holding the back of the seat, and then simultaneously turn the body down into the seat.
Accordingly, there is a need for improved framing systems for human powered vehicles that permit ease of entry and exit, are strong, lightweight and permit adaptation to a wide variety of vehicle systems, including tricycles, water and ice craft and snow craft.